Method of radio communication in a system comprising a plurality of communicating modules

ABSTRACT

A method of radio communication in a system including a plurality of communicating modules, each communicating module being able to obtain at least one measured physical value and to transmit a message encapsulating at least one measured physical value to a hub device according to a given radio communication protocol, the sending of the message being performed during a communication time interval, defined by a start instant and an end instant, a waiting time separating two successive communication time intervals of one and the same communicating module. For each communicating module of the plurality of communicating modules, the waiting time is calculated as a function of an updated counter of the communicating module as a function of a receipt of an acknowledgement message originating from the hub device.

The present invention relates to a method of radio communication in asystem comprising a plurality of communicating modules, and anassociated radio communication system.

The invention lies in the field of wireless communication performed bycommunicating modules, especially in electrical installations, thecommunicating modules being for example modules for measuring one ormore physical quantities of the electrical installation.

There exist short-range radio communication protocols, for exampleBluetooth (trademark) and ZigBee, adapted for domestic networks.

Diverse communicating modules, for example electrical measurementsensors, temperature or pressure sensors, implement the ZigBee protocolbased on the IEEE 802.15.4 communication protocol. The ZigBee protocolexhibits the advantage of reducing the electrical consumption to thestrict minimum, while allowing a low data transmission rate which isnevertheless sufficient for the transmission of equipment measurementand control data.

The objective of the ZigBee Green Power protocol is to allowcommunications between modules with a yet further reduced consumption ofelectricity.

For example, a system for monitoring and managing electricalinstallations is considered, comprising a plurality of communicatingmodules, for example according to the ZigBee Green Power protocol, eachadapted to communicate in a bidirectional manner with a hub device,which receives the totality of the measurement information transmittedby the diverse modules and is adapted to aggregate them for subsequentuse. From the communications point of view, each communicating module isa node of a star network, centred around the hub device.

In such a communications network, one of the problems which arises is toensure that each of the communication nodes can send radio frames ormessages, without interference or collision with one or more other radioframes sent by other nodes, so as to ensure sufficient quality ofservice.

A communication scheme known by the name TDMA (for “Time DivisionMultiple Access”) consists in allocating each node a send time interval,repeated periodically.

Each communicating module forming a node of the communication networkpossesses an internal clock, quartz-based or formed by an RC oscillator,and uses this internal clock to regulate message sends.

However, there is a risk of temporal drift inducing possible temporalsuperpositions of the send intervals associated with distinctcommunication nodes. Such a superposition induces a risk of collision,and consequently of loss of one or more messages.

Moreover, such a scheme requires specific intervention for sequencingthe time intervals when bringing a plurality of communicating modulesinto service.

A conventional protocol, the Aloha protocol, making it possible toensure good quality of service, consists in performing the transmissionby the receiver node of an acknowledgement message (or ACK), and, incase of non-receipt of an acknowledgement message, the sender node waitsa random time before re-sending the initial message.

On the one hand, when the sender nodes are communicating measurementmodules, such as sensors, they do not possess enough energy to remain inpermanent or prolonged reception, therefore the listening periods inreception are reduced.

Moreover, more generally, because of the selection of a random waitingtime, the risk of collision is increased, therefore the communicationssystem is unstable. Moreover, the time required for each node to find anappropriate send time interval may be very long, and does not have anyguaranteed upper limit. Stated otherwise, the system convergence timemay turn out to be long.

The objective of the invention is to remedy the drawbacks of the priorart, so as to improve the quality of service in a communications systemcomprising a plurality of communicating modules.

For this purpose, the invention proposes, according to one aspect, amethod of radio communication in a system comprising a plurality ofcommunicating modules, each communicating module being able to obtain atleast one measured physical value and to transmit a messageencapsulating said at least one measured physical value to a hub deviceaccording to a given radio communication protocol, the sending of themessage being performed during a communication time interval, defined bya start instant and an end instant, a waiting time separating twosuccessive communication time intervals of one and the samecommunicating module. The method is such that for each communicatingmodule of the plurality of communicating modules, the waiting time iscalculated as a function of a counter, updating said communicatingmodule as a function of a receipt of an acknowledgement messageoriginating from the hub device.

Advantageously, the method of the invention makes it possible, by virtueof the use of a counter in each communicating module, to reduce theinstability and to obtain faster convergence.

The radio method of communication according to the invention can alsoexhibit one or more of the features hereinbelow, taken independently oraccording to all technically acceptable combinations.

The counter takes an initial value equal to a predetermined maximumvalue.

Subsequent to a message send and to a receipt of a correspondingacknowledgement message originating from the hub device, the value ofthe counter is decremented by a predetermined decrementation value.

Subsequent to a message send and in the absence of receipt of anacknowledgement message originating from the hub device during acommunication interval, if the value of the counter is strictly lessthan the predetermined maximum value, the value of the counter isincremented by a predetermined incrementation value.

The decrementation value is different from the incrementation value.

The method comprises, subsequent to a message send and to a receipt, bya communicating module, of a corresponding acknowledgement messageoriginating from the hub device, a step, implemented by said receivercommunicating module, of extracting from the acknowledgement message atemporal shift value Δt, positive or negative, to be applied during afollowing send.

The waiting time is equal either to a predetermined communication periodduration if the value of the counter is different from the predeterminedmaximum value, or to said communication period duration increased by arandom additional duration if the value of the counter is equal to thepredetermined maximum value.

The method is implemented by each communicating module supplied by an ACelectrical voltage distribution network of given frequency, andfurthermore comprises a step of detecting timing period as a function ofsaid frequency.

The method comprises the reception of supply voltage values, and foreach voltage value, when said value is greater than a firstpredetermined voltage threshold value or less than a secondpredetermined voltage threshold value, increasing of a synchronizationcounter.

When the synchronization counter reaches a predetermined timing periodcounter value, a timing pulse is sent, said timing pulse serving todetermine the instant of start of communication time interval of thecommunicating module.

According to another aspect, the invention relates to a radiocommunication system comprising a plurality of communicating modules anda hub device, each communicating module being able to obtain at leastone measured physical value and to transmit a message encapsulating saidat least one measured physical value to the hub device according to agiven radio communication protocol, the sending of the message beingperformed during a communication time interval, defined by a startinstant and an end instant, a waiting time separating two successivecommunication time intervals of one and the same communicating module.The system is such that each communicating module of the plurality ofcommunicating modules comprises a unit adapted to calculate the waitingtime as a function of a counter, updating said communicating module as afunction of a receipt of an acknowledgement message originating from thehub device.

The radio communication system according to the invention can alsoexhibit one or more of the features hereinbelow, taken independently oraccording to all technically acceptable combinations.

Each communicating module is a module for measuring electrical values ofan electrical installation.

At least one communicating module supplied by an AC electrical voltagedistribution network of given frequency, and each communicating modulesupplied by the distribution network implements a detection of timingperiod as a function of said frequency and a determination of an instantof start of communication time interval as a function of said timingperiod.

At least one communicating module is adapted to receive anacknowledgement message originating from the hub device and to extractfrom the acknowledgement message a temporal shift value Δt, positive ornegative, to be applied during a following send by said communicatingmodule.

According to another aspect, the invention relates to a computer programcomprising instructions for implementing the steps of a method ofcommunication such as is briefly described hereinabove upon the runningof the program by a processor of a programmable device.

Other features and advantages of the invention will emerge from thedescription given thereof hereinbelow, by way of wholly nonlimitingindication, with reference to the appended figures, among which:

FIG. 1 schematically represents a star communication system in which theradio method of communication according to the invention finds anapplication;

FIG. 2 schematically illustrates a periodic regular allocation ofcommunication time intervals;

FIG. 3 schematically illustrates a collision of communication timeintervals;

FIG. 4 is a synopsis of the main steps of a method of communicationimplemented by a communicating module according to one embodiment;

FIG. 5 schematically illustrates a communicating module according to oneembodiment;

FIG. 6 schematically illustrates the main steps of the synchronizationof communicating modules according to one embodiment;

FIG. 7 schematically illustrates the evolution over time of variables asa function of an AC voltage.

FIG. 1 schematically illustrates a communications system implementing amethod of communication according to the invention.

In this system 1, a plurality of communicating modules, M₁ to M_(n) areable to communicate by a wireless communication protocol with a hubdevice C.

For example, each of the communicating modules is a measurement moduleadapted to measure electrical quantities of an electrical installation,for example the current, the voltage, and to transmit communicationframes, formatted according to a given communication protocol, andencapsulating measured values.

As a variant, other types of communicating modules are present in thesystem 1, for example sensors of current, of energy, of temperature, ofmoisture. Of course, the above list is not exhaustive.

In one embodiment, the communication protocol is the ZigBee Green Powerprotocol.

Each of the communicating modules M₁ to M_(n) is supplied electrically,either by an electrical supply cable conveying electrical energyprovided by a single-phase or three-phase electrical energy provisionnetwork, or by an autonomous electrical energy source, for example acell per communicating module.

The respective electrical supply source of each communicating module isnot illustrated in FIG. 1.

The total number n of communicating modules of the system 1 isarbitrary, for example equal to 20.

The hub device C is preferably wired up so as to be supplied by theelectrical energy provision network (not illustrated in FIG. 1).

Each of the modules M₁ to M_(n) comprises a radio send/receive unit 10 ₁to 10 _(n), adapted to send messages Tx destined for the hub device C,and to receive messages Rx originating from the hub device C.

The messages transmitted and received are formatted according to thechosen communication protocol.

The hub device C comprises a send/receive unit 12, adapted tocommunicate according to the chosen communication protocol with each ofthe send/receive units of each of the modules M₁ to M_(n).

From a communications point of view, the system 1 operates according toa star network architecture, having as central communication node thehub device C, each of the communicating modules forming a communicationnode of the star communications network.

Each of the modules M₁ to M_(n) also comprises a calculation unit 14 ₁to 14 _(n), for example a processor, and a data storage unit 16 ₁ to 16_(n). The calculation 14 _(i) and storage 16 units are able to cooperateto implement a computer program comprising program code instructionsmaking it possible to execute steps of the method of communicationaccording to the invention. Thus, each communicating module is aprogrammable device adapted to implement program code instructions.

The hub device C also comprises a calculation unit 18, for example aprocessor, and a data storage unit 20. The calculation 18 and storage 20units are able to cooperate to implement program code instructionsmaking it possible to execute steps according to one embodiment of themethod of communication according to the invention.

FIG. 2 schematically illustrates the principle of reservation ofcommunication time intervals per communicating module, on a time axis,such as it is known.

For each period of duration ΔT, each communicating module M₁ to M_(n) isallocated a communication interval of duration dt comprising a sendphase, followed, with optionally a waiting period, by a receive phase,also called a listening phase.

For example, the duration dt is of the order of 10 to 40 milliseconds,and the period ΔT is of the order of 5 seconds.

For example, in FIG. 2 have been represented a few communicationintervals: L_(1,1) for the communicating module M₁ during the first sendperiod, L_(1,2) for the communicating module M₁ during the second sendperiod, L_(2,1) for the communicating module M₂ during the first sendperiod, L_(2,2) for the communicating module M₂ during the first sendperiod and so on and so forth.

Each communication interval has a start instant and an end instant,denoted for example t_(n,i) and t_(n,f) for the communicating moduleM_(n).

The communication intervals are regularly distributed over the sendperiod, and spaced temporally so as to decrease the risk of collision.The respective start and end instants are regularly distributed in thisexample.

FIG. 3 illustrates an overlap of the communication intervals associatedwith the respective communicating modules M₁ and M₂. Such an overlap isfor example due to a drift of the internal clocks of the communicatingmodules and induces a significant risk of collision or interferencebetween messages sent respectively by the first communicating module M₁and by the second communicating module M₂. In this case, at least one ofthe messages sent risks being corrupted and therefore unusable.

It is clear that the more the total number n of communicating modulesincreases, the higher the risk of interference.

Conventionally, the hub device C dispatches, via the send/receive unit12, an acknowledgement message (ACK) to the sender communicating modulein case of receipt of an uncorrupted sent message.

As explained in the introduction, preferably, the periods of listeningof the communicating modules are limited, so as to avoid overlysignificant energy consumption.

In case of non-receipt of an acknowledgement message relating to a sentmessage, a known scheme consists in waiting a random time and returningthis message. The instants of start and of end of sending defining thecommunication intervals of the diverse communicating modules are nolonger periodic in time. Such a scheme may induce new collisions, anddoes not make it possible to guarantee the maximum waiting time before asuccessful message dispatch.

FIG. 4 is a synopsis of an embodiment of a method of radio communicationin a system comprising a plurality of communicating modules in anembodiment of the invention.

The method is implemented by each of the communicating modules M₁ toM_(n) of the system considered.

This method makes it possible to manage the selection of thecommunication intervals so as to decrease the risk of collision, whileguaranteeing that a communicating module dispatches a message in a givenmaximum time.

A first step 30 consists in supplying electrical power to the currentcommunicating module M_(k) implementing the method.

Step 30 is followed by a step 32 of initializing a counter, implementedby a variable Counter, to a predetermined maximum value MaxCnt, forexample equal to 10. The value MaxCnt is adjustable to any positiveinteger value, chosen so that the system is stable, for example as afunction of an occupancy rate with respect to the maximum communicationtime for each communicating module.

The value MaxCnt is for example chosen as a function of the number n ofcommunicating modules and of the duration ΔT of a communication period.

During a step 34 of comparison, the value of the variable Counter iscompared with the predetermined value MaxCnt, and it is determinedwhether the variable Counter is different from the predetermined maximumvalue MaxCnt.

In case of difference, step 34 of comparison is followed by a step 36 ofsetting to zero of a variable Jitter representative of the additionalwaiting time before the start instant of a next communication intervalassociated with the current communicating module M_(k).

In case of equality between the value of the variable Counter and of thepredetermined value MaxCnt, step 34 of comparison is followed by a step38 in which the variable Jitter representative of the additional waitingtime before the start instant of a next communication intervalassociated with the current communicating module M_(k) is set to arandom value lying between 0 and ΔT. A random distribution law, forexample a law uniform over the interval [0, ΔT], is applied.

Thereafter in step 40 of determining the waiting time Att_(k), for thecurrent communicating module, before the start instant of a nextcommunication interval, the following calculation formula is applied:

Att _(k) =ΔT+Jitter

Step 40 of determining the waiting time Att_(k) is followed by aneffective waiting step 42, of duration equal to the waiting time Att_(k)determined.

Thereafter, the communicating module M_(k) enters a send and receivecommunication phase 44, for a communication time interval ofpredetermined duration dt.

For example, in an embodiment, the current communicating module M_(k)sends a message containing information in respect of measurements ofcurrent and/or of voltage destined for the hub device, by point-to-pointcommunication, using the ZigBee Green Power protocol, and then waits foran acknowledgement message ACK originating from the hub device.

Under nominal operation, for the time interval of duration dt, thecurrent communicating module sends a message, waits for and receives anacknowledgement message relating to the message sent.

Quite obviously, it is possible to dispatch several messages during thecommunication time interval envisaged.

In the following step 46 of acknowledgement verification it is verifiedwhether the acknowledgement message or each acknowledgement messageenvisaged has been received.

In case of positive verification, therefore if the radio communicationhas operated, step 46 is followed by a step 48 of comparison making itpossible to verify whether the value of the variable Counter is greaterthan zero.

If the value of the variable Counter is strictly greater than zero, step48 is followed by a step 50 of decrementing the variable Counter by apredetermined integer decrementation value Dec. For example, the valueDec is equal to 1.

After step 50, the method returns to step 34 described previously.

If the value of the Counter variable is equal to 0, it is left unchangedand step 48 is followed by step 34 described previously.

In case of negative verification in the reception acknowledgementverification step 46, therefore in the case of collision orinterference, step 46 is followed by a step 52 of comparing the value ofthe variable Counter with the predetermined maximum value MaxCnt, so asto determine whether the value of the variable Counter is strictly lessthan MaxCnt.

If the value of the variable Counter is strictly less than thepredetermined value MaxCnt, then the comparison step 52 is followed by astep 54 of incrementing the value of the variable Counter by apredetermined incrementation value Inc. For example, Inc=2.

Preferably, the incrementation value Inc is different from thedecrementation value Dec, so as to make the value of the variableCounter evolve in a dissymmetric manner as a function of the receipt ornon-receipt of an acknowledgement message.

Advantageously, this makes it possible to avoid remaining in situationsof non-continuous cyclic collisions, for example in case of collisionevery two periods.

In an advantageous embodiment, the incrementation value is greater thanthe decrementation value.

Step 54 is followed by step 34 described previously.

If the value of the variable Counter is equal to the predetermined valueMaxCnt, then step 52 is followed by step 34 described previously. Thus,if the current communicating module has not received any acknowledgementin response to the dispatching of the first message, the value of thevariable Counter remains unchanged.

By applying the method described hereinabove, as soon as the value ofthe variable Counter is different from the predetermined maximum valueMaxCnt, the waiting time of the current communicating module is chosenequal to the period ΔT, without adding an additional random waiting timeJitter.

Advantageously, the method described hereinabove in one of itsembodiments makes it possible to initialize a system comprising aplurality of communicating modules as soon as they are installed,without any prior phase of determining the communication intervalsassociated with each of the nodes when bringing them into service.

Indeed, the proposed method of communication allows automaticconvergence, each communicating module being adapted to find acollision-free communication time interval.

Advantageously, in case of successful reception, the time intervals arerepeated periodically, the waiting time between two time intervals beingequal to ΔT.

In order to further improve the communication between communicatingmodules, whilst limiting the duration of listening for theacknowledgement messages on each communicating module, it is proposed,in an embodiment of the invention, for each communicating modulesupplied electrically by an electrical energy provision network, toregulate the sending of the messages as a function of the frequency ofthe AC current provided by this network, so as to decrease the risk oftemporal drift.

FIG. 5 schematically illustrates a part of a communicating module M_(k)connected via a transmission bus 60 to an electrical energy supplynetwork R, providing an AC voltage, on one or more phase conductors. Thesupply network is therefore either single-phase, or three-phase.

The module M_(k) comprises a unit 62 _(k) for input of AC voltageprovided by the network, for example a 50 Hz voltage, and a unit 64 _(k)for analogue-digital conversion of one phase only of the supply network.

For example, when the supply network is single-phase, the single voltagephase is selected as reference voltage.

When the supply network is three-phase comprising three phase conductorsand a neutral conductor, the voltage of the first phase, denoted V1, isselected as reference voltage. Alternatively, the voltage of the secondor of the third phase are used.

The analogue-digital conversion unit 64 _(k) provides digital voltagesamples V1 to a timing period detection unit 66 _(k) adapted to carryout calculations and to dispatch a timing pulse 68 to the radiosend/receive unit 10 _(k).

For example, a timing pulse 68 is sent every 10 ms for a supply networkfrequency of 50 Hz.

A first, upper voltage threshold value V_(max) and a second, lowervoltage threshold value V_(min) are provided beforehand and stored.

The first voltage threshold value V_(max) is a positive value, and thesecond voltage threshold value V_(min) is a negative value. For examplethese values lie between −80V and +80V. In one embodiment,V_(min)=−V_(max).

Advantageously, the same voltage threshold values V_(max) and V_(min)are stored in each of the communicating modules M₁ to M_(n) of thesystem 1, so as to ensure synchronization between these modules.

FIG. 6 is a synopsis of the main calculation steps implemented by thetiming period detection unit in an embodiment.

During a first initialization step 70, a synchronization counterCounterSync is initialized to zero, and two boolean state variables,called WasPositive and WasNegative are initialized to FALSE.

In the voltage sample reception step 72, a voltage value V is received.

The voltage value V is compared in the comparison step 74 with thefirst, upper voltage threshold value V_(max). If V is greater thanV_(max), step 74 is followed by a step 76 in which the boolean variableWasPositive is set to TRUE.

Step 76 is followed by a step 78 in which it is verified whether theboolean variable WasNegative is equal to TRUE. In case of positivecomparison in step 78, this step is followed by a step 80 in which theboolean variable WasNegative is set to FALSE and the synchronizationcounter CounterSync is increased by 1.

In case of negative comparison in step 78, this step is followed by step72 described previously.

If the voltage value V is less than V_(max), step 74 is followed by astep 82 of comparing the voltage V with the second, lower voltagethreshold value V_(min).

If V is greater than V_(min), step 82 is followed by step 72 describedpreviously.

If V is less than V_(min), step 82 is followed by a step 84 in which theboolean variable WasNegative is set to TRUE.

Step 84 is followed by a step 86 in which it is verified whether theboolean variable WasPositive is equal to TRUE. In case of positivecomparison in step 86, this step is followed by a step 88 in which theboolean variable WasPositive is set to FALSE and the synchronizationcounter CounterSync is increased by 1.

In case of negative comparison in step 86, this step is followed by step72 described previously.

The respective steps 80 and 88 are followed by a comparison 90 of thesynchronization counter with a timing period counter value CPrepresentative of a number of changes of values of states with respectto the values of upper and lower voltage threshold defining a sendperiod.

The timing period counter value is predetermined, for example greaterthan 10, preferably equal to 500.

If in the comparison step 90, the synchronization counter is greaterthan or equal to the timing period counter value CP, a timing pulse issent in step 92, and the synchronization counter is reset to zero instep 94. Otherwise, step 90 is followed by step 72 described previously.

Step 94 is followed by step 72 described previously.

Quite obviously, diverse variants of implementation of a timing perioddetection unit are conceivable.

It should be noted that the synchronization method described withreference to FIG. 6 is applied so as to limit the temporal clock drift,and makes it possible to improve the communication network formed of thehub device and the communicating modules. The improvement is effectivewhatever the scheme for selecting communication time intervalsassociated with each communicating module.

FIG. 7 schematically illustrates the evolution of the voltage selectedas a function of time in a first graph G₁, as well as the first voltagethreshold value V_(max) and the second voltage threshold value V_(min).

Below the graph G₁ are represented two graphs G₂ and G₃ representativeof the values of the boolean variables WasPositive and WasNegative as afunction of time, over several temporal sub-periods.

Finally a last graph G₄ represents the value of the synchronizationcounter CounterSync corresponding to each sub-period.

The graphs G₁ to G₄ are aligned with respect to the abscissa axis (timeaxis) which comprises, in the example of FIG. 7, five sub-periods SP₁ toSP₅, the synchronization counter being increased at each of thesub-periods, each sub-period corresponding to a change of state of thevoltage signal with respect to the voltage threshold values V_(max) andV_(min).

Advantageously, each communicating module implements such a timingperiod detection unit based on one and the same voltage value obtainedfrom the supply network, thereby making it possible to synchronize thecommunicating modules and to limit the clock drift.

Moreover, advantageously, the implementation of such a unit, for eachcommunicating module supplied with electricity by the distributionnetwork, makes it possible to preserve the synchronization of thecommunicating modules even in case of stoppage of the hub device.

However, in certain installations, all or some of the communicatingmodules are not supplied by the electrical supply network, but thesemodules comprise an autonomous power supply.

In this case, as an alternative, it is envisaged to dispatchsynchronization or re-synchronization information to the communicatingmodules connected on the basis of the hub device.

In this alternative embodiment, the hub device uses the bidirectionalcommunication with each of the communicating modules.

The hub device uses its own internal clock, or an external clock tocalculate, on receipt of a message originating from a givencommunicating module M_(k), a temporal shift Δt, positive or negative,to be applied by the communicating module M_(k) during a following send.

The temporal shift, with an associated sign to indicate whether it is alead or a lag, is dispatched by the hub device to the communicatingmodule, preferably in the message containing the acknowledgement ACK ofreceipt.

The recipient communicating module M_(k) is then able to extract thistemporal shift information from the message received and to store it soas to apply the temporal shift indicated during a following send.

This is a method of master-slave synchronization in a network with startopology, the master device being the hub device.

Furthermore, the hub device can, by this same method of dispatching atemporal shift Δt to be applied, dispatch instructions to re-arrange theorder of the communication time intervals associated with thecommunicating modules, in such a way that sends of correlatedmeasurement information are grouped together temporally. For example, inan application, it is beneficial to group together an information item,transmitted by a first module, in respect of current and an informationitem, transmitted by a second module, in respect of temperature, thecorresponding measurements being performed substantially at the sametime, so as to obtain at intervals of a few milliseconds thesecorrelated information items.

In another embodiment, certain of the communicating modules of acommunication system are supplied by autonomous energy sources, andother modules are supplied by an electrical energy supply network. Inthis embodiment, the diverse embodiments of the invention that weredescribed hereinabove are combined, so as to allow each communicatingmodule to determine the optimized communication intervals for avoidingpossible collisions or interference.

1. A method of radio communication in a system comprising a plurality ofcommunicating modules, each communicating module being able to obtain atleast one measured physical value and to transmit a messageencapsulating said at least one measured physical value to a hub deviceaccording to a given radio communication protocol, the sending of themessage being performed during a communication time interval, defined bya start instant and an end instant, a waiting time separating twosuccessive communication time intervals of one and the samecommunicating module: wherein each communicating module of the pluralityof communicating modules, the waiting time is calculated as a functionof an updated counter of said communicating module as a function of areceipt of an acknowledgement message originating from the hub device.2. The method of communication according to claim 1, wherein saidcounter takes an initial value equal to a predetermined maximum value.3. The method of communication according to claim 2, wherein, subsequentto a message send and to a receipt of a corresponding acknowledgementmessage originating from the hub device, the value of the counter isdecremented by a predetermined decrementation value.
 4. The method ofcommunication according to claim 3, wherein, subsequent to a messagesend and in the absence of receipt of an acknowledgement messageoriginating from the hub device during a communication interval, if thevalue of the counter is strictly less than the predetermined maximumvalue, the value of the counter is incremented by a predeterminedincrementation value.
 5. The method of communication according to claim4, wherein the decrementation value is different from the incrementationvalue.
 6. The method of communication according to claim 2, comprising,subsequent to a message send and to a receipt, by a communicatingmodule, of a corresponding acknowledgement message originating from thehub device, a step, implemented by said receiver communicating module,of extracting from the acknowledgement message a temporal shift valueΔt, positive or negative, to be applied during a following send.
 7. Themethod of communication according to claim 2, wherein the calculatedwaiting time is equal either to a predetermined communication periodduration if the value of the counter is different from the predeterminedmaximum value, or to said communication period duration increased by arandom additional duration if the value of the counter is equal to thepredetermined maximum value.
 8. The method of communication according toclaim 1, implemented by each communicating module supplied by an ACelectrical voltage distribution network of given frequency, furthermorecomprising a step of detecting timing period as a function of saidfrequency.
 9. The method of communication according to claim 8,comprising the reception of supply voltage values, and for each voltagevalue, when said value is greater than a first predetermined voltagethreshold value or less than a second predetermined voltage thresholdvalue, increasing of a synchronization counter.
 10. The method ofcommunication according to claim 9, wherein when the synchronizationcounter reaches a predetermined timing period counter value, a timingpulse is sent, said timing pulse serving to determine the instant ofstart of communication time interval of the communicating module.
 11. Acomputer program comprising instructions for implementing the steps of amethod of communication in accordance with claim 1 upon the running ofthe program by a processor of a programmable device.
 12. A radiocommunication system comprising a plurality of communicating modules anda hub device, each communicating module being able to obtain at leastone measured physical value and to transmit a message encapsulating saidat least one measured physical value to the hub device according to agiven radio communication protocol, the sending of the message beingperformed during a communication time interval, defined by a startinstant and an end instant, a waiting time separating two successivecommunication time intervals of one and the same communicating module,wherein each communicating module of the plurality of communicatingmodules comprises a unit adapted to calculate the waiting time as afunction of a counter, updating said communicating module as a functionof a receipt of an acknowledgement message originating from the hubdevice.
 13. A communication system according to claim 12, wherein eachcommunicating module is a module for measuring electrical values of anelectrical installation.
 14. The communication system according to claim12, wherein at least one communicating module supplied by an ACelectrical voltage distribution network of given frequency, and whereineach communicating module supplied by the distribution networkimplements a detection of timing period as a function of said frequencyand a determination of an instant of start of communication timeinterval as a function of said timing period.
 15. The communicationsystem according to claim 12, wherein at least one communicating moduleis adapted to receive an acknowledgement message originating from thehub device and to extract from the acknowledgement message a temporalshift value Δt, positive or negative, to be applied during a followingsend by said communicating module.